This invention relates to automatic die casting machines and, in particular, to horizontal rotary die casting machines which are used to cast rotors for electric motors or the like.
More particularly, this invention relates to an improved die cast machine for automatically casting rotors in a minimum amount of time. The machine is arranged to simultaneously perform a plurality of operations or functions at three stations. The functions or operations to be performed at each of the stations are arranged to optimize the operating speed of the machine.
Conventional die casting machines generally include stationary front and back plates and a movable or traveling plate which is reciprocably mounted between the two stationary plates. The relative positions of the stationary plates are maintained by a plurality of tie bars which extend between the two stationary plates. Die halves are fastened to the front plate and the traveling plate, respectively, and the traveling plate is extended and retracted to respectively close and open the die. After the die is closed, molten metal is injected into the die to form a die cast part. After a part is thus formed, the die is opened by retracting the traveling die and, after the traveling plate has moved a predetermined distance, bumper pins which are slidably mounted in apertures located both in the die and the traveling plate engage a bumper plate which is located behind the traveling plate. These bumper pins engage and eject the die cast part from the portion of the die which is attached to the traveling plate. After the die cast part is removed from the die casting machine, the excess metal, generally referred to as a sprue or runner system, is removed from the die cast part in a separate pressing machine called a trim press.
Other prior art die casting machines incorporate the trimming operation in the die casting machine. In this type of machine, an indexing apparatus rotates the die cast part between a casting station and a trimming station in the die casting machine. Further, in die casting conventional parts, the cast part is usually attached to the indexing mechanism by the sprue which is formed in die casting the part. The die cast part is then rotated to the trimming station where the sprue is removed.
One application for die casting machines involves casting a rotor of an electrical motor. In this type of application, the body of the motor comprises a stack of circular plates or laminations which are secured together by a temporary skew pin inserted through aligned central openings in the laminations. The die casting machine is employed for casting the connector bars and end rings of the rotor assembly. An indexing apparatus first picks up the rotor body at a loading station and then moves it to a casting station where the connector bars and end rings are formed. The rotor is then carried through a cooling station, and the temporary skew pins are ejected from the cast rotor. Finally, the rotor is removed from the machine. At some point, the sprue or runner system is removed from the completed rotor and returned to a waste container for reuse.
In most prior art die casting machines, molten material, usually zinc, aluminum, or magnesium, is injected into the die in one of two ways. In one method, the molten material is conveyed to the part periphery and is injected into the side of the die cavity, thereby leaving a runner attached to the side of the cast part. This is called "side gate casting." In another method, the molten metal is injected into the ends of the die cavity through inwardly tapered cone-shaped openings in the die plate. Such openings have a small diameter on the side of the die plate adjacent the interior of the die cavity. This method is called "pin-point gating" because the runner system is attached to the molded part only by means of narrow necks or pin points of molded material which may be broken away to remove the runner system from the cast part.
In yet another prior art die casting machine, a six station indexing mechanism is mounted between two stationary plates for moving a part in rotary fashion through a plurality of spaced stations. One operation is performed at each station. A toggle linkage mechanism moves a traveling plate alternately forward and away from the indexing mechanism. A disadvantage of this prior art automatic indexed multistation die casting machine is that the time required for casting a rotor is longer than desired. By arranging the machine so that six stations are provided, the factor which limits the speed of the machine is the longest time required for completing one of the six operations. Thus this arrangement limits the indexing speed of the machine to the completion of the operation which requires the greatest amount of time. Furthermore, in this prior art machine, a separate ejector mechanism is provided, thus adding further to the length of time required for casting and ejecting a rotor and further adding to the complexity of the machine.
Additionally, since in prior art die casting machines a relatively heavy tooling section, such as the traveling plate, is moved over a relatively large distance for closing the die prior to casting a part, the long stroke for the traveling plate requires additional time for completion of one cycle of the machine, thereby adversely affecting the productivity of the machine.
Still further, the prior art die casting machines do not provide full compensation to account for various rotor stack heights. Thus, such prior art die casting machines are limited to casting rotors of a certain minimum stack height or require the manual insertion or removal of spacer plates to cast rotors of various stack heights, which is time consuming and therefore undesirable.
It is therefore desired to provide an improved automatic die casting machine that is particularly suitable for casting rotors for electric motors and wherein the cycle time of the machine is minimized. It is furthermore desired to provide such a machine which includes a full range of compensation. Lastly, it is desired to provide such a machine wherein the movable die cast portion is secured to a small movable platen which operates over a short distance and is clamped by means of hydraulic clamping cylinders.